1. Field of the Invention
The present invention relates to a power steering system wherein power assistance derived therefrom will be modulated according to a vehicle condition such as vehicle speed.
2. Description of the Prior Art
In maneuvering a steering wheel of an automotive vehicle, it is recognized that power assistance at high vehicle speeds may desirably be less than at low speeds to allow for stabilization of the steering wheel at high speeds.
A power steering system with the above-mentioned steering characteristics is known having a reaction device that is supplied with a fluid pressure which is increased as the vehicle speed increases, thus applying a hydraulic reaction or feeling to the steering wheel. In such prior system, an additional fluid pump which is driven at a rate proportional to vehicle speed is provided to supply the reaction device with fluid pressure proportional to vehicle speed. As a result, it is difficult to control the pressure of the fluid as freely as desired or according to other vehicle conditions such as rotational angle and rotational speed of the steering wheel.